On Fri, 19 Nov 2004 15:20:17 +0000, Phil Addison wrote:
On Fri, 19 Nov 2004 15:05:35 -0000, "IMM" wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
IMM wrote:
Yes,why oh why do combi installers chuck out a perfectly usable
cylinder,especially in large family houses?. My view for family
properties is to keep the cylinder,feed it from the combi,obviously
make sure things are well insulated/controlled.
This that is your view you should change it, as the cylinder will burst.
Strange. I know of one system
snip tripe
Please do not comment on fields you have no experience of.
How about attempting top answer the actual original question?
Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me
IME experience there are several reasons why (ordinary) combi boilers have poor
regulation of DHW temperature.
1) Drawing off water from elsewhere especially in the same dwelling.
2) Thermostatic mixing valves fighting the boiler.
but mainly:
3) When the DHW exchanger becomes scaled up the heat transfer rate becomes
limited, that's bad enough. Eventually the heat transfer rate drops below
the lowest modulated setting of the burner (typically around 10-12kW on a
popular 24kW unit), at this point the control system, in order to modulate
the burner further has to start switching it on an off. Given the
considerable thermal inertia of the components a fluctuation of the output
temperature begins.
1. Can be mitigated by good design and practice. Namely don't fit a combi
where the supply is inadequate. Take it's supply upstream of other
draw offs (even consider putting a slight restriction on the feed to
everything except the combi.
2. This is not a common problem and shoudl be mitigated by getting 1 and 3
right.
3. Descale or replace secondary heat exchanger.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at
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